Energy generation and storage has long been a subject of study and development. Of special import is the storage of energy in a compact form that can be easily charged and discharged, such as rechargeable batteries and/or capacitors. The components of these various systems have been generally optimized by seeking to achieve the maximum stored energy density. However, most, if not all, commercially-available systems yield far less than their theoretical energy density. One such energy storage system utilizes activated carbon electrodes to store charge. One example of an activated carbon electrode system is a double layer capacitor system described in U.S. Pat. No. 3,536,963. The mechanism for energy storage is based on the formation of an electrical double layer at the interface between an activated carbon electrode and a supporting electrolyte under an applied electrical field. Double layer capacitors will accept and store significant amounts of energy at a wide variety of potentials, unlike batteries where a given threshold voltage must be exceeded. Optimization of this type of system is based upon enhancing the charge storage capacity of the activated carbon electrode. Double layer capacitors can exhibit a capacity equivalent to tens of farads per gram of activated carbon when the activated carbon has a surface area in excess of 1000 square meters per gram (m.sup.2 /g). However, this system has limited application because the energy density needs to be even greater, and efforts have been made to coat metal or metal oxides on the carbon surface to increase the energy density and conductivity of the electrode. Coating electrochemically active metals on carbon combines the advantages of the metal's good conductivity and electrochemical activity with carbon's high surface area. Those familiar with catalysis will appreciate that carbon is often used as a support structure upon which metal is coated directly to form a catalyst. Techniques such as electroplating and vacuum deposition (e.g. sputtering, evaporation, etc.) have been used to coat the particles. However, electroplating metal on carbon is very difficult due to the porous structure of the carbon, which causes a non-uniform current distribution and results in a relatively poor metal-carbon bond. The use of metals and polymers mixed with activated carbon was demonstrated in a 1983 patent by the Lucas Research Centre, England (UK Patent 2054252B). This patent discloses a pressed plate secondary zinc electrode containing 16 to 50% graphite, 0.5 to 10% polytetrafluoroethylene (PTFE) and small amounts of heavy metal oxides (e.g. HgO, PbO, and CdO). The optimum mixture was found to be 32% graphite, 5% PTFE, 62% ZnO and 1% metallic oxides. However, these electrodes were simply physical mixtures of the various ingredients, and they too suffered from the inability to utilize all of the available surface area of the carbon.
Clearly, it would be desirable to form an electrode that exhibits increased charge storage capacity, thus further enabling the miniaturization of energy storage devices.